Week 3

Question 1

If you are looking at a wiggly line what is the wavelengths?

Answer 1

the difference in distance between the peaks

Question 2

What is an example of a long and a short wavelength?

Answer 2

Long - radio/microwave - size of a building-butterfly

Short- Gamma ray or x-ray - size of atmoic nuclei-atoms

Question 3

What is the colour relationship for long and short wavelengths?

Answer 3

Only a small visible range

Question 4

What is the relationship between temperature and wavelength

Answer 4

cooler objects emit longer wavelenths, hotter objects emit shorter wavelengths

Question 5

What kind of radiation can penetrate the earths atmosphere and what is in the grey and what can;t

Answer 5

CAN
Radio and infrared-visible

MAYBE
Some radio and some infrared

CANNOT
microwave and vible-gamaray short wave

Question 6

What is Planck’s law

Answer 6

Hotter objects emit more radiation - higher specific spectral emittance

hotter objects emit short wave radiation and more radiation overall

the peak wavelength at which objects emit decreases with increasing temperature

Question 7

What does the sun emit?

Answer 7

the peak is in the visible part of the spectrum

Question 8

What kind of wavelength does the earth emit

Answer 8

the earth is colder the sun, emits in the infrared part of the spectrum

Question 9

what percentage of the suns energy does the earth absorb and reflect?

Answer 9

70% absored
30% relected- espeically by light surfaces like clouds, snow and deserts

Question 10

What is the unit of mesurement for radiative fluxes

Answer 10

W/m^2

the flow of energy through a given surface area over a certain amount of time

Question 11

What is the global-mean incoming solar radiation and what is the net-absorbed solar radiation

Answer 11

global-mean incoming solar radaition = 340W/M^2

net-absorbed solar radiation is 240w/m^2

Question 12

What is a radiative balance and how is it achieved?

Answer 12

energy in= energy out

emissions of infrared radiation to space

Question 13

Without the atmosphere what temperature would the earth be?

Answer 13

-19oc

Question 14

Without the ghg effect whast would the earth temperature be?

Answer 14

15oc

Question 15

What is the Co2 content of the atmosphere for Earth and Venus?

Answer 15

.02% = earth
96% Venus

Question 16

What is the ghg effect?

Answer 16

radiation emitted by earth is trapped by gases in the atmosphere and re-emitted in all directions

when it is re-emitted down this is the greenhouse effect

the large up and down longwave fluxes

idea that there is an asymmetry between absorption by ghg of infrared and visible radiation- traps infra-red

Question 17

What is albedo?

Answer 17

the reflection of solar energy depends on the albedo the earth atmosphere

high albedo - light reflective surfaces like snow and clouds
low albedo - dark surfaces like water and forests

Question 18

How do you calculate albedo?

Answer 18

albedo= reflected solar radiation/incoming solar radiation
1= everything is reflected 0= nothing is reflected

Question 19

What is the earths mean albedo

Answer 19

30%

however this varies spatially and depends on the surface type

Question 20

Where is shortwave radiation absorbed

Answer 20

mainly at the surface - some in the atmosphere but this is more UV rather than visible

Ozone layer - absorbs harmful carcogenic UV - holes in the ozone due to man-made CFCs

Question 21

Why are there different amounts of emission from different parts of the atmosphere

Answer 21

due to temperature changes - but what matters is the emissions out to space
typical level that escapes to space has a temperature that corresponds to that emission

Question 22

What is water vapour opque to?

Answer 22

infrared radiation at many wavelengths - therefore it absorbs it

Question 23

Why is there so much focus on carbon dioxide

Answer 23

it stays for longer in the atmosphere and thermodynamically unreative - very stable molecule once produced it will remain for a long time

Question 24

Methane from? and how much in the atmosphere?

Answer 24

gas leaks and livestock

has more than doubled

Question 25

Where is N2O from?

Answer 25

industrial processes, cars and fertilizers

Question 26

What does the absoption of radiation by ghg depend on?

Answer 26

the wavelength of infra red radiation

related to the molecular structure of the gases

Question 27

What is the water vapour window?

Answer 27

a range of wavelengths where eart is able to emit radiation to space.

Co2 is important as it partially masks the water vapour window - a range of wavelengths where the earth is able to emit to space

Increasing CO2 concentration partially close this window
- blocks more of the watervapour window

Question 28

What are sensible and latent heat fluxes?

Answer 28

Sensible heat is temperature - idea of a direct exchange of heat

Latent heat is humidity - like evaporation requires energy, condensation and then heating.

idea of fluxes by conduction and convection

Question 29

What does a postive imbalance mean for the earth?

Answer 29

the earth is absorbing more than it emits

the imbalance is mainly due to the strengthening of the greenhouse effect - though there are additional feedbacks

Question 30

What is radiative forcing?

Answer 30

an externally imposed instantaneous perturbation to the radiative balance - instantaneous perturbation

relative to some reference state it is measured by W/m^2

can be natural such as the sun’s orbit or human such as Co2
can be perturbing the energy in (solar radiation in) or energy out (how much escapes to space)

Question 31

Can you talk me through how GHG are a radative forcing?

Answer 31

Start in a radiative balance of the same amount of energy going in and out

increase in the amount of GHG means there is in>out - radiative forcing

the earth will accumulate heat thus warm

warming allows the earth to emit more radiative - Plancks Law

this continues until energy out is large enough - then a new equilibrium is reached

Question 32

Can you give some examples of forcings

Answer 32

Anthropogenic
- aerosol emissions - can reflect or absorb solar radiation
- land use change - surface albedo – contrails from airplanes

Natural
- solar activity variations
- volanic forcings - negative becausing of dimming aerosols -but these are v shortlived 2-3 yrs

Question 33

From the AR5 report what is the main forcing

Answer 33

Co2

methane and aerosol also have a substantial effect but large uncertainties around aerosols and clouds

Question 34

What is the effect of aerosols on the atmosphere?

Answer 34

Most have a cooling effectas they directly reflect sunlight or promote the formation of white clouds

however, black carbon has a warming effect as it absorbs sunlight in the atmosphere

there are large regional and temporal differences in aerosol production due to patterns of industry

they don’t mix well in the atmosphere so are quite localised in their effect

Question 35

If there is suddenly a doubling of the CO2 what would the temperature response look like on a graph?

what about the radiative imbalance line?

Answer 35

Temp
It would be flat until the forcing point then gradually and in a curve warm - and then stablise - initially fsater and then increasingly slowly as it plateus

exponential to begin with then decay to equilibrium

Radiative balance
- sharp increase at forcing point and then a gradual decline to equilibrium
proportional to the temperature change

Plancks law. idea that there is a relationship between temp and wavelength and the net energy emissions -as temperature increases earth radiates more energy and decreases the energy imbalance

Question 36

what is the energy budget equation ?

Answer 36

Radiative Imbalance = N

Radiative forcing = F (initial forcing)

Radiative response = § (or teepee, trainge T)

N= F-§

Question 37

What happens if F>0

Answer 37

the earth needs to warm in order to emit more infrared energy to space and re-establish a balance and vice versa (F<0 is a cooling)

Question 38

Would a postive forcing cool or warm

Answer 38

warming